Many halogenated organic chemical contaminants present in the environment are known to be highly resistant to degradation. Current research has demonstrated that their persistence in the environment may be overcome by initially subjecting these contaminants to dehalogenation reactions. Once dehalogenated, the organic contaminants are usually degraded easily, generally by aerobic microbial processes.
Dehalogenation of organic contaminants in microbial ecosystems occurs both by enzymatic and non-enzymatic mechanisms. An example of a non-enzymatic mechanism is the reductive dechlorination of DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane) by an iron porphyrin redox system wherein the DDT is reacted with a reduced iron porphorin such as hematin. Most enzymatic reactions involve whole microbial cells such as bacteria, fungi and algae. Enzymatic reactions are usually more specific than non-enzymatic reactions but their activity is destroyed by harsh conditions such as exposure to high temperatures.
Microbial activity can assist dehalogenation of organic contaminants either directly by enzyme production, or indirectly, by maintaining the reducing conditions of the environment and thereby enhancing the inorganic and biochemical mechanisms.